Interesting triggers have terenas.i find two.
if you get humans and get any undead unit, this unit if standing by terenas(neutral yellow), terenas dying,if artas standing by terenas(maybe any neutral status terenas, need test, yellow neutral work), terenas joining to you army. I experimented a little. I became interested in this mechanic after Wrynn
(The Archmage is his trigger and if wrynn neutral red that not problem him joining )joining my army in the first game in this map. It became interesting with how many neutral heroes have this triggers and what is needed for this.
(Edit add):
And i have one more question, Where to get recipes, I couldn't find them